Effect Of Dietary Energy Feeding Level Or Sources On Onset Of Puberty, Follicular Quality And The Mechanism Investigation In Gilts

The main objective of the present study was to investigate the effects of dietary energy feeding levels and sources on puberty onset, follicular development and the associative changes of kiss-1/GPR54expressions in hypothalamus of developing gilts, hoping to provide theory for nutritional regulation of puberty onset and follicular development, and optimize the nutritional regiment for rearing developing gilts. Three experiments were conducted to achieve this objective. In experiment1, anestrus gilts by nutrient restriction were used to examine the nutritional effects on the puberty onset and reproductive maturation and the underlying mechanisms. Experiment2was conducted to investigate30%limited energy intake of NRC (1998) requirement on the puberty onset, follicular development, and changes of gene expressions of hypothalamic Kiss-1/GPR54system. In experiment3, under similar dietary energy feeding level, effects of dietary energy sources (starch rich, fat rich or soluble fiber rich diets) on age at puberty, follicular development and gene expressions of kiss-1/GPR54in hypothalamus in gilts.Experiment1Effects of nutrient restriction on puberty onset, follicular development and the underlying mechanisms in giltsTwenty LY gilts with similar bodyweight (122±4.5kg) and age (230±6d) having experienced two estrus cycles were fed a normal (CON,2.86kg/d) or nutrient restricted (NR, lkg/d) food regimens to expect the nutritionally induced anestrus. Nutritional regimen was started on the day of occurrence of the second standing heat. Blood samples were collected at the beginning of experiment and at3days’interval for measurement of progesterone concentrations when gilts failed to express estrus behavior. Gilts were defined anestrus if progesterone concentrations of consecutive3blood samples were below1.0ng/mL in nutrient restricted gilts. Both groups of gilts were slaughtered on the day of estrus of CON gilts, and tissue samples from hypothalamus-pituitary-gonadal axis were collected for detection of gene expressions. Results:1) NR gilts experienced another three estrus cycles, but did not express estrus symptoms at the anticipated6th estrus. Individual progesterone concentrations in NR gilts were below1.0ng/mL, ovaries from nutrient-restricted gilts were found to have normal completion of luteal phase, but corpora lutea was not formed, which was reflection of nutritionally induced anestrus.2) NR gilts had decreased bodyweight and backfat thickness by30.8%and50%(P<0.05) on d88of experiment, and significantly impaired development of reproductive tract, the uterus weight, individual length of uterine horn, length of oviduct were decreased by83.2%,46.1%and32.8%, respectively.3) Circulating concentrations of IGF-Ⅰ, kisspeptin, estradiol, progesterone and leptin were significantly lower in NR gilts than CON gilts (P<0.05), and nutrient restriction down-regulated gene expressions of kiss-1, G-protein coupled protein54, gonadotropin-releasing hormone, estrogen receptor a, progesterone receptor, leptin receptor, follicle-stimulating hormone and luteinizing hormone and insulin-like growth factor I in hypothalamus-pituitary-gonadal axis of gilts.Collectively, nutrient restriction resulted in cessation of estrus cycle and impairment of reproductive function, which was likely due to abnormal hormone secretions and kissl/GPR54gene expressions in hypothalamus.Experiment2Effects of dietary energy feeding level on age at puberty, follicular development, and gene expressions of kiss-1/GPR54in hypothalamus in giltsForty LY gilts with similar bodyweight (55±4.5kg) and age (104±6d) were fed a basal diet containing70%of recommended dietary digestive energy (LE,70%NRC level), or basal diets supplemented with additional oil to meet NRC level (HE, NRC level). When4gilts in HE group reached puberty onset, they were slaughtered along with their counterparts in LE groups. Results:1) LE gilts reached puberty12±2.3days later than HE gilts.2) LE gilts had significantly lower bodyweight and P2thickness by17.7%and23.0%. Average daily gain were0.66±0.02VS0.89±0.05,0.56±0.04VS0.87±0.07, and0.63±0.02VS0.84±0.05kg/d, for55-100kg phase,100kg-puberty phase,55kg-puberty phase, respectively, compared with HE gilts.3) LE gilts had significantly lower circulating IGF-I, leptin and E2concentrations compared with HE gilts.4) LE gilts had significantly decreased length of uterine horns, ovary weight, number of large follicles and weight of follicular fluid.5) LE gilts had decreased mRNA expressions of Era, kiss-1and GnRH in AVPV and Obr in ARC, and mRNA expressions of LH and IGF-Ⅰ, and mRNA expressions of IGF-Ⅰ R and ObR were significantly lowered in LE gilts.These results demonstrated that low energy feeding delayed age at puberty and follicular development, and was associated with decreased leptin, IGF-1and E2 seretions, and decreased gene expressions of hypothalamic kiss-1and GnRH and pituitary LH.Experiment3Effects of dietary energy source on age at puberty, follicular development and gene expressions of kiss-1/GPR54in hypothalamus in giltsAccording to single factor experiment design, sixty LY gilts with similar bodyweight (57±4.5kg) and age (106±6d) were fed starch-rich (S), fat-rich (F) or fat and fiber-rich (FP) diets. Gilts were fed two phases of diets for55-100kg phase and100kg-puberty phase. Gilts were fed corn-soybean meal-based diets added with additional starch (591g/d for phase Ⅰ and745g/d starch for phase Ⅱ), additional soybean oil (270g/d for phase I and340g/d for phase Ⅱ), and additional oil and pectin (270g/d fat+35g/d pectin for phase Ⅰ, and340g/d fat+30g/d pectin for phase Ⅱ) for S, F and FP gilts, respectively. Gilts on the19th day of2nd estrus cycle were slaughtered. Results:1) Dietary energy source influenced the age at puberty, F gilts reached puberty12±2.1and7.7±2.3days earlier than S and FP gilts.2) Circulating leptin and E2concentrations in F gilts were higher than S gilts, but circulating IGF-Ⅰ and follicular E2and IGF-Ⅰ were lower in F gilts than S gilts. Circulating leptin, IGF-I and E2in FP gilts were lower in FP gilts than that in F gilts. Number of large follicles (20.5±0.8VS17.5±0.6) and number of corepus luteum (16.7±1.0VS14.3±0.8) was higher in FP gilts than F gilts.3) mRNA expressions of Era, kiss-1, GPR54and GnRH in hypothalamic AVPV were lowest in gilts fed diets contained pectin. mRNA expressions of ObR, kiss-1, GPR54and GnRH in hypothalamic ARC were highest in gilts fed oil rich diets. mRNA expressions of LH and IGF-1R in pituitary were highest in gilts fed starch rich diets. mRNA expressions of FSH in pituitary were highest in gilts fed diets contained pectin. mRNA expression of IGF-Ⅰ R was down-regulated in F gilts compared with S and PF gilts, but mRNA expression of ObR was up-regulated in F gilts compared with S and PF gilts.These results demonstrated that starch rich diet could improve follicular development, fat rich diet could facilitate puberty onset, pectin rich diet could enhance ovulation rate.Overall conclusion:1) Dietary energy induced changes of the blood hormone secretions, expressions of kiss-1/GPR54in hypothalamic ARC and AVPV, and GnRH, FSH and LH to regulate the puberty onset and follicular development.2) Starch-rich, fat-rich and fiber-rich diet could improve reproductive performance of gilts through improved follicular development, puberty onset, and ovulation rate.